Terrestrial Communications Networks That Transmit Using Circular Polarization

ABSTRACT

A terrestrial communications network may be configured to wirelessly communicate with a plurality of radiotelephones. The terrestrial communications network may include a plurality of base stations that are configured to wirelessly communicate with the plurality of radiotelephones. Moreover, the plurality of base stations may include at least one base station that is configured to transmit information to at least one radiotelephone using a circularly polarized antenna. Related methods are also discussed.

RELATED APPLICATIONS

This application claims the benefit of priority as a divisional of U.S.application Ser. No. 10/880,023, filed Jun. 28, 2004, entitled SystemsAnd Methods For Modifying Antenna Radiation Patterns Of Peripheral BaseStations Of A Terrestrial Network To Allow Reduced Interference whichclaims the benefit of: provisional Application No. 60/490,638, filedJul. 28, 2003, entitled Systems and Methods for Modifying AntennaRadiation Patterns of Peripheral Base Stations of an AncillaryTerrestrial Component to Allow Reduced Interference; and of provisionalApplication No. 60/492,710, filed Aug. 5, 2003, entitled AdditionalSystems And Methods For Modifying Antenna Radiation Patterns OfPeripheral Base Stations Of An Ancillary Terrestrial Component To AllowReduced Interference. All of the above referenced patent applicationsare assigned to the assignee of the present application, and thedisclosures of all of the above referenced patent applications arehereby incorporated herein by reference in their entirety as if setforth fully herein.

FIELD OF THE INVENTION

This invention relates to wireless communications systems and methods,and more particularly to terrestrial cellular communications systems andmethods.

BACKGROUND

Satellite radiotelephone communications systems and methods are widelyused for radiotelephone communications. Satellite radiotelephonecommunications systems and methods generally employ at least onespace-based component, such as one or more satellites that areconfigured to wirelessly communicate with a plurality of satelliteradiotelephones.

A satellite radiotelephone communications system or method may utilize asingle antenna beam covering an entire area served by the system.Alternatively, in cellular satellite radiotelephone communicationssystems and methods, multiple beams are provided, each of which canserve distinct geographical areas in the overall service region, tocollectively serve an overall satellite footprint. Thus, a cellulararchitecture similar to that used in conventional terrestrial cellularradiotelephone systems and methods can be implemented in cellularsatellite-based systems and methods. The satellite typicallycommunicates with radiotelephones over a bidirectional communicationspathway, with radiotelephone communication signals being communicatedfrom the satellite to the radiotelephone over a downlink or forwardlink, and from the radiotelephone to the satellite over an uplink orreturn link.

The overall design and operation of cellular satellite radiotelephonesystems and methods are well known to those having skill in the art, andneed not be described further herein. Moreover, as used herein, the term“radiotelephone” includes cellular and/or satellite radiotelephones withor without a multi-line display; Personal Communications System (PCS)terminals that may combine a radiotelephone with data processing,facsimile and/or data communications capabilities; Personal DigitalAssistants (PDA) that can include a radio frequency transceiver and apager, Internet and/or intranet access, Web browser, organizer, calendarand/or a global positioning system (GPS) receiver; and/or conventionallaptop and/or palmtop computers or other appliances, which include aradio frequency transceiver. Radiotelephones may also be referred toherein as “radioterminals” or simply “terminals”.

As is well known to those having skill in the art, terrestrial networkscan enhance cellular satellite radiotelephone system availability,efficiency and/or economic viability by terrestrially reusing at leastsome of the frequency bands that are allocated to cellular satelliteradiotelephone systems. In particular, it is known that it may bedifficult for cellular satellite radiotelephone systems to reliablyserve densely populated areas, because the satellite signal may beblocked by high-rise structures and/or may not penetrate into buildings.As a result, the satellite band spectrum may be underutilized orunutilized in such areas. The use of terrestrial retransmission of allor some of the satellite band frequencies can reduce or eliminate thisproblem.

Moreover, the capacity of the overall system can be increasedsignificantly by the introduction of terrestrial retransmission, sinceterrestrial frequency reuse can be much denser than that of asatellite-only system. In fact, capacity can be enhanced where it may bemostly needed, i.e., in and/or proximate to densely populated urban,industrial, and/or commercial areas. As a result, the overall system canbecome much more economically viable, as it may be able to serve a muchlarger subscriber base. Finally, satellite radiotelephones for asatellite radiotelephone system having a terrestrial component withinthe same satellite frequency band and using substantially the same airinterface for both terrestrial and satellite communications can be morecost effective and/or aesthetically appealing. Conventional dual bandand/or dual mode alternatives, such as the well known Thuraya, Iridiumand/or Globalstar dual mode satellite and/or terrestrial radiotelephonesystems, may duplicate some components, which may lead to increasedcost, size and/or weight of the radiotelephone.

U.S. Pat. No. 6,684,057 issued Jan. 27, 2004, to the present inventorKarabinis, and entitled Systems and Methods for Terrestrial Reuse ofCellular Satellite Frequency Spectrum, the disclosure of which is herebyincorporated herein by reference in its entirety as if set forth fullyherein, describes that a satellite radiotelephone frequency can bereused terrestrially by an ancillary terrestrial network even within thesame satellite cell, using interference cancellation techniques. Inparticular, the satellite radiotelephone system according to someembodiments of U.S. Pat. No. 6,684,057 includes a space-based componentthat is configured to receive wireless communications from a firstradiotelephone in a satellite footprint over a satellite radiotelephonefrequency band, and an ancillary terrestrial network that is configuredto receive wireless communications from a second radiotelephone in thesatellite footprint over the satellite radiotelephone frequency band.The space-based component also receives the wireless communications fromthe second radiotelephone in the satellite footprint over the satelliteradiotelephone frequency band as interference, along with the wirelesscommunications that are received from the first radiotelephone in thesatellite footprint over the satellite radiotelephone frequency band. Aninterference reducer is responsive to the space-based component and tothe ancillary terrestrial network that is configured to reduce theinterference from the wireless communications that are received by thespace-based component from the first radiotelephone in the satellitefootprint over the satellite radiotelephone frequency band, using thewireless communications that are received by the ancillary terrestrialnetwork from the second radiotelephone in the satellite footprint overthe satellite radiotelephone frequency band.

United States Patent Application Publication No. 2003/0054761 A1,published Mar. 20, 2003 to the present inventor Karabinis and entitledSpatial Guardbands for Terrestrial Reuse of Satellite Frequencies, thedisclosure of which is hereby incorporated herein by reference in itsentirety as if set forth fully herein, describes satelliteradiotelephone systems that include a space-based component that isconfigured to provide wireless radiotelephone communications in asatellite footprint over a satellite radiotelephone frequency band. Thesatellite footprint is divided into a plurality of satellite cells, inwhich satellite radiotelephone frequencies of the satelliteradiotelephone frequency band are spatially reused. An ancillaryterrestrial network is configured to terrestrially reuse at least one ofthe ancillary radiotelephone frequencies that is used in a satellitecell in the satellite footprint, outside the cell and in someembodiments separated therefrom by a spatial guardband. The spatialguardband may be sufficiently large to reduce or prevent interferencebetween the at least one of the satellite radiotelephone frequenciesthat is used in the satellite cell in the satellite footprint, and theat least one of the satellite radiotelephone frequencies that isterrestrially reused outside the satellite cell and separated therefromby the spatial guardband. The spatial guardband may be about half aradius of a satellite cell in width.

United States Patent Application Publication No. US 2003/0054815 A1,published Mar. 20, 2003 to the present inventor Karabinis, and entitledMethods and Systems for Modifying Satellite Antenna Cell Patterns inResponse to Terrestrial Reuse of Satellite Frequencies, the disclosureof which is hereby incorporated herein by reference in its entirety asif set forth fully herein, describes that space-based wirelessradiotelephone communications are provided in a satellite footprint overa satellite radiotelephone frequency band. The satellite footprint isdivided into satellite cells in which satellite radiotelephonefrequencies of the satellite radiotelephone frequency band are spatiallyreused. At least one of the satellite radiotelephone frequencies that isassigned to a given satellite cell in the satellite footprint isterrestrially reused outside the given satellite cell. A radiationpattern of at least the given satellite cell is modified to reduceinterference with the at least one of the satellite radiotelephonefrequencies that is terrestrially reused outside the given satellitecell.

SUMMARY

According to embodiments of the present invention, a communicationssystem may include a terrestrial network having a plurality of basestations providing communications service for radioterminals over aterrestrial network coverage area. The plurality of base stations mayinclude interior base stations providing communications service forradioterminals in an interior portion of the terrestrial networkcoverage area and peripheral base stations providing communicationsservice for radioterminals at a peripheral portion of the terrestrialnetwork coverage area. Moreover, at least one of the peripheral basestations may provide transmissions directed toward an interior portionof the terrestrial network coverage area with greater power thantransmissions directed away from interior portions of the terrestrialnetwork coverage area.

The peripheral base stations and/or interior base stations may define aportion of a perimeter of the terrestrial network coverage area suchthat interior base stations of the terrestrial network are located onone side of the perimeter and not on the other side of the perimeter. Inaddition, the perimeter may be closed surrounding interior portions ofthe terrestrial network coverage area. Moreover, at least one of theinterior base stations may define a plurality of sectors surrounding theinterior base station(s), and transmissions may be directed from theinterior base station(s) to each of the sectors so that transmissionsare directed over a 360 degree pattern surrounding the interior basestation.

At least one peripheral base stations may define a plurality of sectorssurrounding the peripheral base station(s), and the peripheral basestation(s) may provide transmissions to at least one sector directedsubstantially toward an interior portion of the terrestrial networkcoverage area with greater power than toward another sector directedsubstantially away from interior portions of the terrestrial networkcoverage area. At least one peripheral base station(s) may includedirectional transmission antenna(s) for sector(s) directed substantiallytoward interior portions of the terrestrial network coverage area butnot for the sector(s) directed substantially away from interior portionsof the terrestrial network coverage area. In addition, at least oneperipheral base station(s) may include directional receive antenna(s)directed to at least one of the sectors surrounding the peripheral basestation(s). Moreover, at least one peripheral base station(s) may havefewer transmit sectors, fewer transmit antenna elements, differenttransmit antenna elements, and/or different transmit gain patterns thanat least one interior base station.

The communications system may also include a second terrestrial networkhaving a second plurality of base stations providing communicationsservice for radioterminals over a second terrestrial network coveragearea, and a no-service region may separate the first and secondterrestrial network coverage areas. Accordingly, communications servicesmay not be provided by base stations of either of the first or thesecond terrestrial networks in the no-service region.

In addition, the communications system may include a space based networkincluding at least one satellite. The space based network may providecommunications service for radioterminals in a first satellite coveragearea using at least a first frequency of a satellite frequency band, andthe space based network may provide communications service forradioterminals in a second satellite coverage area using at least asecond frequency of the satellite frequency band. Moreover, at least aportion of the terrestrial network coverage area may be within the firstsatellite coverage area, and an entirety of the terrestrial networkcoverage area may be outside the second satellite coverage area. Inaddition, at least one of the base stations of the terrestrial networkmay provide communications service using the second frequency of thesatellite frequency band, and at least one of the base stations may notprovide communications to and/or from the radioterminals receivingcommunications from the base stations, using the first frequency of thesatellite frequency band.

The space based network may transmit communications to radioterminals inthe first satellite coverage area using the first frequency, and thespace based network may transmit communications to radioterminals in thesecond satellite coverage area using the second frequency. Moreover, theat least one of the base stations of the terrestrial network maytransmit communications using the second frequency. In addition, thespace based network may receive communications from radioterminals inthe first satellite coverage area using at least a third frequency. Thespace based network may receive communications from radioterminals inthe second satellite coverage area using at least a fourth frequency, atleast one of the base stations of the terrestrial network may receivecommunications using the fourth frequency, and at least one of the basestations of the terrestrial network may not receive communications fromthe radio terminals receiving communications from the base stations ofthe terrestrial network, using the third frequency.

The terrestrial network may also include a plurality of receive-onlybase stations configured to receive communications from radioterminalsat the peripheral portion of the terrestrial network coverage area.Accordingly, communications service for a radioterminal may be providedby a receive-only base station receiving communications from theradioterminal and by another base station transmitting communications tothe radioterminal.

According to additional embodiments of the present invention, acommunications system may include a terrestrial network having aplurality of base stations providing communications service forradioterminals over a terrestrial network coverage area. The pluralityof base stations may include interior base stations providingcommunications service for radioterminals in an interior portion of theterrestrial network coverage area and peripheral base stations providingcommunications service for radioterminals at a peripheral portion of theterrestrial network coverage area. Moreover, at least one of theperipheral base stations may be a receive-only base station that doesnot transmit.

The peripheral base stations and/or interior base stations may define aportion of a perimeter of the terrestrial network coverage area suchthat interior base stations of the terrestrial network are located onone side of the perimeter and not on the other side of the perimeter. Inaddition, the perimeter may be closed surrounding interior portions ofthe terrestrial network coverage area. Moreover, at least one interiorbase station(s) may define a plurality of sectors surrounding theinterior base station(s), and transmissions may be directed from atleast one interior base station(s) to each of the sectors so thattransmissions are directed over a 360 degree pattern surrounding atleast one interior base station(s). At least one peripheral basestation(s) may define a plurality of sectors surrounding the peripheralbase station(s), and at least one peripheral base station(s) may includedirectional reception antenna(s) for at least one of the sectors.

The communications system may also include a second terrestrial networkhaving a second plurality of base stations providing communicationsservice for radioterminals over a second terrestrial network coveragearea. Moreover, a no-service region may separate the first and secondterrestrial network coverage areas such that communications services arenot provided by base stations of either of the first or the secondterrestrial networks in the no-service region. In addition, thecommunications system may also include a space based network having atleast one satellite. The space based network may provide communicationsservice for radioterminals in a first satellite coverage area using atleast a first frequency of a satellite frequency band, and the spacebased network may provide communications service for radioterminals in asecond satellite coverage area using at least a second frequency of thesatellite frequency band. Moreover, at least a portion of theterrestrial network coverage area may be within the first satellitecoverage area, and an entirety of the terrestrial network coverage areamay be outside the second satellite coverage area. In addition, at leastone of the base stations may provide communications service using thesecond frequency of the satellite frequency band, and at least one ofthe base stations may not provide communications to and/or from theradioterminals receiving communications from the base stations, usingthe first frequency of the satellite frequency band.

The space based network may transmit communications to radioterminals inthe first satellite coverage area using the first frequency, and thespace based network may transmit communications to radioterminals in thesecond satellite coverage area using the second frequency. Moreover, theat least one of the base stations of the terrestrial network maytransmit communications using the second frequency. The space basednetwork may receive communications from radioterminals in the firstsatellite coverage area using at least a third frequency, and the spacebased network may receive communications from radioterminals in thesecond satellite coverage area using at least a fourth frequency. Inaddition, at least one of the base stations of the terrestrial networkmay receive communications using the fourth frequency, and at least oneof the base stations of the terrestrial network may not receivecommunications, from the radio terminals receiving communications fromthe base stations, using the third frequency.

According to still additional embodiments of the present invention, acommunications system may include a terrestrial network having aplurality of base stations providing communications service forradioterminals over a terrestrial network coverage area. The pluralityof base stations may include interior base stations providingcommunications service for radioterminals in an interior portion of theterrestrial network coverage area and peripheral base stations providingcommunications service for radioterminals at a peripheral portion of theterrestrial network coverage area. In addition, at least one of theperipheral base stations may be substantially disabled for transmissionaway from interior portions of the terrestrial network coverage area.

The peripheral base stations and/or the interior base stations maydefine a portion of a perimeter of the terrestrial network coverage areasuch that interior base stations of the terrestrial network are locatedon one side of the perimeter and not on the other side of the perimeter.Moreover, the perimeter may be closed surrounding interior portions ofthe terrestrial network coverage area.

At least one of the peripheral base stations may have fewer transmitsectors, fewer transmit antenna elements, different transmit antennaelements, and/or different transmit gain patterns than at least one ofthe interior base stations. Moreover, at least one of the interior basestations may transmit and receive communications, and at least one ofthe peripheral base stations may be a receive-only peripheral basestation. The communications system may also include a second terrestrialnetwork having a second plurality of base stations providingcommunications service for radioterminals over a second terrestrialnetwork coverage area. In addition, a no-service region may separate thefirst and second terrestrial network coverage areas such thatcommunications services may not be provided by base stations of eitherof the first or the second terrestrial networks in the no-serviceregion.

The communications system may also include a space based network havingat least one satellite. The space based network may providecommunications service for radioterminals in a first satellite coveragearea using at least a first frequency of a satellite frequency band, andthe space based network may provide communications service forradioterminals in a second satellite coverage area using at least asecond frequency of the satellite frequency band. At least a portion ofthe terrestrial network coverage area may be within the first satellitecoverage area, and an entirety of the terrestrial network coverage areamay be outside the second satellite coverage area. Moreover, at leastone of the base stations may provide communications service using thesecond frequency of the satellite frequency band, and at least one ofthe base stations may not provide communications to and/or from theradioterminals receiving communications from the base stations, usingthe first frequency of the satellite frequency band.

At least one of the peripheral base stations may provide transmissionsdirected toward an interior portion of the terrestrial network coveragearea with greater power than transmissions directed away from interiorportions of the terrestrial network coverage area. At least one of theperipheral base stations may be a receive-only base station that doesnot transmit.

According to yet additional embodiments of the present invention,methods of providing communications for radioterminals may includeproviding communications service for radioterminals at an interiorportion of a terrestrial network coverage area using interior basestations. Communications service may be provided for radioterminals at aperipheral portion of the terrestrial network coverage area usingperipheral base stations. More particularly, at least one of theperipheral base stations may provide transmissions directed toward aninterior portion of the terrestrial network coverage area with greaterpower than transmissions directed away from interior portions of theterrestrial network coverage area.

According to more embodiments of the present invention, methods ofproviding communications for radioterminals may include providingcommunications service for radioterminals at an interior portion of aterrestrial network coverage area using a plurality of interior basestations. Communications service may be provided for radioterminals at aperipheral portion of the terrestrial network coverage area using aplurality of peripheral base stations wherein at least one of theperipheral base stations is a receive-only base station that does nottransmit.

According to still more embodiments of the present invention, methods ofproviding communications for radioterminals may include providingcommunications for radioterminals at an interior portion of aterrestrial network coverage area using a plurality of interior basestations. Communications may be provided for radioterminals at aperipheral portion of the terrestrial network coverage area using aplurality of peripheral base stations wherein at least one of theperipheral base stations is substantially disabled for transmission awayfrom interior portions of the terrestrial network coverage area.

According to yet more embodiments of the present invention, acommunications system may include a plurality of interior down-linktransmitters configured to transmit communications to radioterminalslocated in interior portions of a terrestrial network coverage area. Aplurality of interior up-link receivers may be configured to receivecommunications from radioterminals located in the interior portions ofthe terrestrial network coverage area. In addition, a plurality ofperipheral up-link receivers may be configured to receive communicationsfrom radioterminals located in a peripheral region of the terrestrialnetwork coverage area adjacent the interior portions of the terrestrialnetwork coverage area, wherein at least a portion of the peripheralregion is outside an engineered coverage area of any down-linktransmitters of the communications system.

Some embodiments of the present invention provide an AncillaryTerrestrial Component (ATC) that is configured to wirelessly communicatewith a plurality of radioterminals using at least one satelliteradiotelephone frequency over an ATC service area. The ATC includes aplurality of base stations that are configured to wirelessly communicatewith the plurality of radioterminals using at least one satelliteradiotelephone frequency. The plurality of base stations includes atleast one interior base station that is located in an interior portionof the ATC service area, and at least one peripheral base station thatis located at a periphery of the ATC service area. In some embodiments,at least one peripheral base station has fewer transmit sectors, fewertransmit antenna elements, different transmit antenna elements and/ordifferent transmit gain patterns than at least one interior basestation. In other embodiments, at least one interior base station is atleast one transmit and receive interior base station, and the ATCfurther includes at least one receive-only peripheral base station.Thus, systems and methods are provided for modifying antenna radiationpatterns of peripheral base stations of an ancillary terrestrialcomponent, compared to interior base stations, to allow reducedinterference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating portions of a terrestrial networkaccording to first embodiments of the present invention.

FIG. 2 is a diagram illustrating portions of a terrestrial networkaccording to second embodiments of the present invention.

FIG. 3 is a diagram illustrating a terrestrial network according tothird embodiments of the present invention.

FIG. 4 is a diagram illustrating satellite and terrestrialcommunications networks sharing a satellite frequency band according tofourth embodiments of the present invention.

FIG. 5 is a diagram illustrating a terrestrial network according tofifth embodiments of the present invention.

FIG. 6 is a diagram illustrating satellite and terrestrialcommunications networks sharing a satellite frequency band according tosixth embodiments of the present invention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

It will be understood that although the terms first, second, etc. areused herein to describe various elements, these elements should not belimited by these terms. These terms are only used to distinguish oneelement or embodiment from another element or embodiment. Thus, a firstelement or embodiment below could be termed a second element orembodiment, and similarly, a second element or embodiment may be termeda first element or embodiment without departing from the teachings ofthe present invention. As used herein, the term “and/or” includes anyand all combinations of one or more of the associated listed items.Moreover, as used herein, “substantially the same” band means that thebands substantially overlap, but that there may be some areas ofnon-overlap, for example at the band ends. Moreover, “substantially thesame” air interface(s) means that the air interfaces are similar butneed not be identical. Some changes may be made to one air interface(i.e., a satellite air interface) relative to another (i.e., aterrestrial air interface) to account for different characteristics thatmay exist between the terrestrial and satellite communicationsenvironments. For example, a different vocoder rate may be used forsatellite communications compared to the vocoder rate that may be usedfor terrestrial communications (i.e., for terrestrial communications,voice may be compressed (“vocoded”) to approximately 9 to 13 kbps,whereas for satellite communications a vocoder rate of 2 to 4 kbps, forexample, may be used). In addition or in alternatives, different forwarderror correction coding, different interleaving depth, and/or differentspread-spectrum codes may be used, for example, for satellitecommunications compared to the coding, interleaving depth, and/or spreadspectrum codes (i.e., Walsh codes, long codes, and/or frequency hoppingcodes) that may be used for terrestrial communications.

Moreover, as used herein, a “substantially southern” or a “substantiallynorthern” direction means a direction that includes a component in asouthern or northern direction, respectively. For example, asouthwestern direction may be a substantially southern direction.

Satellite systems that may operate co-frequency (also referred to asco-channel) with at least some frequencies of a satellite systemcontaining an Ancillary Terrestrial Component (ATC) may receiveco-frequency (co-channel) interference from the co-frequency(co-channel) operations of the ATC. To reduce the level of co-frequency(co-channel) interference that may be generated by an ATC, the ATC basestations may be engineered with X dB (e.g., 18 dB) of in-buildingpenetration signal margin, such as, for example, X dB of in-buildingpenetration return-link signal margin. This signal margin may enable anATC radioterminal (i.e., a radioterminal that is communicating with anATC) to operate even when it is subjected to X dB of structural signalattenuation and may also facilitate a reduction of the radioterminal'soutput signal power when the radioterminal is being subjected to lessthan X dB of structural signal attenuation. In the limit, as theradioterminal is not being subjected to any structural signalattenuation (the radioterminal is entirely in the clear) the signalpower that the radioterminal may radiate in order to communicate with abase station may be reduced by as much as X dB (e.g., 18 dB) relative tomaximum. This can reduce the level of interference that may be sensed bya co-frequency (co-channel) satellite system.

As used herein, the term Ancillary Terrestrial Component (ATC) may referto one or more terrestrial base stations in a terrestrial network ofbase stations providing communications service for radioterminals over aterrestrial network coverage area (also referred to as an ATC servicearea). For example, the term Ancillary Terrestrial Component may referto a single terrestrial base station, with a plurality of suchterrestrial base stations providing service for radioterminals over acoverage area of a terrestrial network (referred to as an AncillaryTerrestrial Network (ATN)).

Cellular and PCS systems are routinely deployed in urban areas withsignificant in-building signal penetration margins, typically rangingbetween 15 to 20 dB. Engineering an ATC with X dB (e.g., 18 dB) ofstructural attenuation signal margin may be accomplished by using one ofa plurality of established statistical design methodologies that areknown to those skilled in the art. In accordance with an example of sucha design methodology and as an initial step, the link budget of a basestation, and corresponding radioterminal equipment, may be calculatedand balanced, bi-directionally, by taking into account some or allrelevant base station, radioterminal, and/or propagation environmentparameters such as the maximum Effective Isotropic Radiated Power (EIRP)of the base station and radioterminal equipment, the propagationexponent factor appropriate for the ATC environment, signal attenuationdue to multipath fading, receiver sensitivities of base station andradioterminal, base station and/or radioterminal antenna gain anddiversity reception gain factor, etc., including a signal loss of X dB(e.g., 18 dB) due to structural attenuation. The bi-directionallybalanced link budget can identify an estimate of the service radius of abase station. At this service radius a radioterminal may communicatewith a base station, with certain probability of success, subject to theassumed link budget parameter values and propagation impairmentsincluding the effect of one or more signal attenuating structures thatmay, in the aggregate, impose X dB (e.g., 18 dB) of additional signalattenuation beyond that imposed by the propagation loss (as defined, forexample, by the conventional Cost 231-Hata model) and multipath fadingloss. It follows that when a radioterminal is not subject to any signalattenuating structures, it can, subject to closed-loop power control,radiate at a reduced signal power level that averages X dB (e.g., 18 dB)lower than its maximum.

An ATC service area may comprise an ensemble of ATC base stations thatmay be engineered and deployed based on the above design principles. Insuch an environment, as an active radioterminal migrates from one ATCbase station service area to another, the system may continue to provideservice to the radioterminal via the ATC base station that can nominallyprovide the highest signal quality and/or strength to thatradioterminal. As such, a radioterminal that is transitioning from theservice area of one ATC base station to another and is operating outsidethe influence of any signal attenuating structures may, on average,continue to radiate at a reduced signal power level of X dB (e.g., 18dB) less than its maximum.

According to some embodiments of the present invention, in the proximityof a perimeter of an ATC service area, the ATC may be configured toreduce, completely avoid and/or substantially minimize servingradioterminals that may be beyond the engineered service area of a basestation and may thus radiate a higher level of power. This may beaccomplished, according to some embodiments, by configuring and/ororienting the antenna elements of a base station to substantiallyilluminate only certain directions that, according to a link budget, maysatisfy the X dB (e.g., 18 dB) structural attenuation signal marginconfiguration design of an ATC. Thus, for example, at least one ATC basestation proximate to a perimeter of an ATC service area may beconfigured with a reduced (fewer) number of sectors, reduced (fewer)antenna elements and/or different antenna elements, and may thus not becapable of providing service in at least one direction, to substantiallythe same radius as in another direction.

Thus, as shown in FIG. 1, an ATC includes a plurality of base stationsthat are configured to wirelessly communicate with a plurality ofradioterminals using at least one satellite radiotelephone frequency.The plurality of base stations include at least one interior basestation 10, that is located at an interior portion of the ATC servicearea, and at least one peripheral base station 20 that is located at aperimeter 30 of the ATC service area. As shown in FIG. 1, at least oneperipheral base station 20 has fewer sectors, fewer antenna elements,different antenna elements and/or different gain patterns than at leastone interior base station 10. For example, as shown in FIG. 1, at leastsome of the interior base stations 10 have complete 360° coverage using,for example, three sectors, whereas at least one of the peripheral basestations 20 have a reduced number of sectors, such as one or twosectors.

It will be understood by those having skill in the art that, althoughFIG. 1 depicts a single row of peripheral base stations 20 adjacent theperimeter 30 of the ATC service area, more than one row of peripheralbase stations may be provided. It also will be understood that, in someembodiments, only a single sector may be provided for the perimeter basestations 20. In still other embodiments, a complete set of sectors, suchas three sectors, may be provided, with reduced numbers of antennaelements, reduced antenna gain, and/or reduced EIRP in one or more ofthe sectors, compared to the interior base stations 10. Combinations ofthese embodiments also may be provided. Moreover, each peripheral basestation need not include the same (reduced) number of sectors and/orantenna elements, and not all peripheral base stations 20 need includefewer sectors, fewer antenna elements, different antenna elements,and/or different (reduced) EIRP. In some embodiments, the perimeter basestations 20 may communicate with an interior base station 10. In otherembodiments, the peripheral base stations 20 may communicate with an ATCinfrastructure.

In still other embodiments of the present invention, in lieu of, or incombination with, the ATC configuration of FIG. 1, at least onereceive-only base station may be provided proximate to a perimeter of anATC footprint, that may have been engineered in accordance with a linkbudget inclusive of X dB (e.g., 18 dB) of structural signal attenuation,so as to maintain the emissions of a radioterminal substantially inaccordance with a reduced power level criterion as the radioterminalcontinues to operate outside of the engineered service footprint of theATC.

Thus, as shown in FIG. 2, at least one peripheral ATC base station maybe a receive-only base station 40, which may include the same number ofsectors and/or receive antenna elements as the interior ATC basestations 10 or, as shown in FIG. 2, may include fewer sectors, fewerreceive antenna elements and/or different receive antenna elementscompared to the interior ATC base stations 10. It also will beunderstood that, as with the reduced sector and/or reduced antennaelement peripheral base stations 20 of FIG. 1, the receive-only basestations 40 of FIG. 2 need not be identical in their number of sectorsand/or antenna elements, and more than one row of receive-only basestations 40 may be provided. Moreover, at least some of the receive-onlybase stations 40 may communicate with an adjacent or non-adjacentinterior ATC base station 10 or may communicate with the ATCinfrastructure. Moreover, combinations of peripheral base stations 20and 40 of FIGS. 1 and 2 may be provided according to other embodimentsof the present invention.

Accordingly, embodiments of the present invention provide a plurality ofbase stations that are configured to wirelessly communicate with aplurality of radioterminals using at least one satellite radiotelephonefrequency. The plurality of base stations include at least one interiorbase station that is located in an interior portion of the ATC servicearea and at least one peripheral base station that is located at aperiphery of the ATC service area. At least one peripheral base stationhas fewer sectors, fewer antenna elements, different antenna elements,different gain patterns, and/or different EIRP than at least oneinterior base station. In other embodiments, at least one interior basestation is at least one transmit and receive interior base station, andthe ATC further includes at least one receive-only peripheral basestation.

Other embodiments of the present invention can configure at least oneperipheral base station 20 of an ATC, at the perimeter or fringes 30 ofan ATC service area to reduce or avoid serving radioterminals that arebeyond its engineered service footprint. This may be accomplished in avariety of ways including orienting some sectors of base stations toilluminate areas that are within the ATC service footprint whiledisabling other sectors that may illuminate areas away from the ATCservice footprint. Such disabled sectors can be configured asreceive-only sectors. In some embodiments, the signals that are receivedat a receive-only sector may also be received by at least one othertransmit and receive sector and may be combined, using conventionaltechniques.

As such, a radioterminal that may be drifting away from the core ATCservice footprint, while continuing to communicate with a base stationby receiving on the side-lobes of an enabled sector, may transmit backto that base station via the main lobe (or substantially via the mainlobe) of a receive-only sector that is oriented toward it. In thisconfiguration, the forward link to the radioterminal generally will be amuch weaker link than the return link, and service to that radioterminalgenerally will terminate due to forward link “breakage” before theradioterminal is at a distance that may require it to radiate maximum ornear maximum power. Thus, a sharp decrease in base station forward-linksignal power may be established at an edge of an ATC service area byjudiciously configuring the sectors of base stations 20 that are at ornear the edge.

The front-to-back EIRP ratio of an ATC base station antenna may be, perthe ATC Rules, approximately 25 dB (see 47 CFR 25.253 (e)). Thus, a basestation that is located at (or near) the edge of an ATC servicefootprint can have at least one of its (typically three) sectorstransmit-disabled. In other words, the sector(s) that would have pointedaway from the ATC service footprint can be disabled in their ability totransmit. For such a base station, a user who is in an un-served area(an area that would have been served by one of the transmit-disabledsectors) generally will experience significant forward-link signalattenuation (of the order of 25 dB) relative to a user who is at thesame distance from the base station tower and within a transmit-enabledsector. With a forward link disadvantage of approximately 25 dB, thebase station service radius in the direction of a receive-only sectormay shrink to less than two tenths of what it would have been otherwise.It follows that, in some embodiments, a radioterminal that is within areceive-only sector and outside the influence of any signal attenuatingstructures may radiate, subject to closed-loop power control,approximately 25 dB less than it would have radiated at the edge of asymmetrically engineered ATC sector.

According to additional embodiments of the present invention, asillustrated in FIG. 3, a terrestrial communications network 100 mayinclude a plurality of interior and peripheral base stations 110 a-h and120 a-o respectively providing communications service for radioterminals150 over a terrestrial network coverage area. The interior base stations110 provide communications service for radioterminals 150 in an interiorportion of the terrestrial network coverage area, and the peripheralbase stations 120 provide communications service for radioterminals atperipheral portions of the terrestrial network coverage area. Moreparticularly, at least one of the peripheral base stations 120 mayprovide transmissions directed toward an interior portion of theterrestrial network coverage area with greater EIRP (power) thantransmissions directed away from interior portions of the terrestrialnetwork coverage area. For example, at least one of the peripheral basestations may have fewer transmit sectors, fewer transmit antennaelements, different transmit and/or receive antenna elements, and/ordifferent transmit and/or receive gain patterns and/or parameters thanat least one of the interior base stations.

More particularly, at least one interior base station(s) 110 may definea plurality of sectors surrounding the interior base station, and atleast one interior base station(s) 110 may direct transmissions to allsectors surrounding the respective interior base station(s) so thattransmissions are directed over a 360 degree pattern surrounding therespective interior base station(s). For example, one of the interiorbase stations may include directional transmit antennas configured toprovide transmissions over a 120 degree sector, and the base station mayinclude at least three such directional antennas so that transmissionsare directed over three 120 degree sectors to cover a 360 degree patternsurrounding the base station. In addition or in an alternative, one ormore interior base stations 110 may include omnidirectional antennasand/or directional antennas. At least one of the interior base stationsmay also be configured so that transmissions are directed to a patternof less than 360 degrees surrounding the at least one interior basestation. Transmission patterns and/or sectors are not shown for theinterior base stations 110 of FIG. 3 for the sake of clarity.

As discussed above, at least one of the peripheral base stations 120 mayprovide transmissions directed toward an interior portion of theterrestrial network coverage area with greater EIRP (power) thantransmissions directed away from interior portions of the terrestrialnetwork coverage area. More particularly, at least one of the peripheralbase stations may include one or more directional transmit antennas eachproviding transmissions to a sector, such as a 120 degree sector.Moreover, the directional transmit antenna(s) on a peripheral basestation 120 may be oriented such that transmissions from the peripheralbase station 120 are directed over a sector (or sectors) orientedsubstantially toward interior portions of the terrestrial networkcoverage area with greater EIRP (power) than is directed over a sector(or sectors) oriented substantially away from interior portions of theterrestrial network coverage area.

By way of example, the peripheral base stations 120 may respectivelyinclude one or more directional transmit antennas configured to providetransmissions to a respective 120 degree transmit sector 121 a-o or 122c or 122 n. In the example of FIG. 3, for the base stations 120 a-b, 120d-m, and 120 o, one or more directional transmit antennas at each basestation may be configured to provide transmissions to radioterminals ina single respective 120 degree sector 121 a-b, 121 d-m, and 120 o.Moreover, for the base stations 120 c and 120 n, directional transmitantennas at each base station may be configured to provide transmissionsto radioterminals in two respective 120 degree sectors 121 c, 122 c, 121n, and 122 n. Accordingly, the peripheral base stations 120 a-o maydefine a perimeter 125 (illustrated by the dotted line of FIG. 3) of theterrestrial network coverage area such that interior base stations 110are located on one side of the perimeter 125 and not on the other sideof the perimeter 125. As illustrated by the dotted line of FIG. 3, theperimeter 125 may substantially follow boundaries of sectors to whichthe peripheral base stations 120 transmit. The transmit sectors of theperipheral base stations may define the peripheral portions of theterrestrial network coverage area, and areas bounded by the peripheralportions may define the interior portions of the terrestrial networkcoverage area.

In addition, the peripheral base stations 120 a-o may includedirectional receive antennas defining receive coverage sectors that spana full 360 degree pattern surrounding each of the peripheral basestations. For example, the peripheral base stations 120 a-b, 120 d-m,and 120 o may include directional transmit antennas that substantiallytransmit to a single respective 120 degree sector 121 a-b, 121 d-m, and121 o, without substantially transmitting to sectors covering theremaining 240 degrees surrounding the base station. Similarly, theperipheral base stations 120 c and 120 n may include directionaltransmit antennas that substantially transmit to two 120 degree sectorswithout substantially transmitting to the remaining 120 degree sectorsurrounding the base station. The peripheral base stations, however, mayinclude directional receive antennas configured to receivecommunications from radioterminals in the sectors 121 a-o and 122 c and122 n to which the peripheral base stations transmit as well asdirectional receive antennas configured to receive communications fromradioterminals in sectors to which the peripheral base stationssubstantially do not transmit. In an alternative or in addition, one ormore of the peripheral base stations may include one or moreomnidirectional receive antenna(s).

Accordingly, interior and exterior base stations 110 and 120 may providecommunications services for radioterminals in a coverage area and/orsector thereof using, for example, air interface protocols and/orarchitectures such as FDM/FDMA (frequency division multiplexed/multipleaccess), TDM/TDMA (time division multiplexed/multiple access), CDM/CDMA(code division multiplexed/multiple access), and/or OFDM/OFDMA(orthogonal frequency division multiplexed/multiple access). Moreover,the base stations of the terrestrial communications network 100 mayemploy a frequency reuse and/or spreading code reuse pattern to increasean efficiency of frequency usage and/or capacity and/or reduceinterference. For example, each base station may have a relatively smallcoverage area and/or sector and adjacent base stations and/or sectorsmay use different frequencies and/or spreading codes to reduceinterference therebetween.

Communications for a radioterminal 150 a in an interior portion of theterrestrial network coverage area may be provided by an interior basestation 110 c as illustrated in FIG. 3. As the radioterminal 150 achanges position within the terrestrial network coverage area during acommunication such as a radiotelephone conversation, communicationsservices for the radioterminal 150 a may be handed off from one sectorof base station 110 c to another sector of base station 110 c, and/or tosectors of other interior or peripheral base stations.

Communications for a radioterminal 150 b in the peripheral portion ofthe terrestrial network coverage area may be provided by a peripheralbase station 120 g. As the radioterminal 150 b is in the sector 121 g,to which transmit and receive antennas of the base station 120 g aredirected, communications can be provided for the radioterminal 150 bwithin the sector 121 g. Moreover, communications services for theradioterminal 150 b may be handed off from the base station 120 g to anadjacent interior or peripheral base station if the radioterminal 150 bmoves from the sector 121 g to a sector of another base station.

As shown in FIG. 3, the sectors of peripheral base stations may appearto have fixed boundaries defined by the transmit sectors of therespective transmit antennas. As will be understood, however, side lobesof the radiation patterns generated by the directional transmit antennasof the peripheral base stations may have sufficient energy to supportacceptable link transmissions to a radioterminal 150 c outside theperimeter 125 of the terrestrial network coverage area and outside thesector 121 f of the peripheral base station 120 f. As discussed above,the peripheral base station 120 f may include receive antennas, thatmay, for example, be directional, supporting robust link reception ofcommunications from the mobile terminal outside sector 121 f.

Accordingly, communications service for the radioterminal 150 c mayinitially be provided by the base station 120 f within sector 121 f, butthe radioterminal 150 c may then move outside the sector 121 f and awayfrom the terrestrial network coverage area. According to embodiments ofthe present invention, down-link transmissions from the base station 120f to the radioterminal 150 c may continue to be provided by thedirectional antenna(s) servicing the sector 121 f, and the quality ofthe down-link communications received by the radioterminal 150 c mayrapidly deteriorate. A relatively high quality of up-link communicationsreceived by the base station 120 f from the radioterminal 150 c,however, may be maintained as the radioterminal 150 c moves outsidesector 121 f, because the base station 120 f includes receive antennascovering a full 360 degree pattern surrounding the base station 120 f.Accordingly, communications service for the radioterminal 150 c willmost likely be terminated due to deterioration in the down-link from theperipheral base station 120 f to the radioterminal before significantdeterioration in the up-link from the radioterminal 150 c to the basestation 120 f occurs which may cause the radioterminal to radiate at, ornear, maximum power.

By providing sectors outside the perimeter 125 wherein a peripheral basestation can receive via antennas operative in these sectors up-linkcommunications from a radioterminal without transmitting communicationsto the radioterminal via antennas operative in these sectors,communications with the radioterminal may be terminated without causingthe radioterminal to increase its transmit power to a maximum, or near amaximum before termination. More particularly, in a closed loop powercontrol system, the base station may request that the radioterminalincrease its transmission power as the signal strength and/or quality ofcommunications received by the base station decreases, and similarly,the radioterminal may request that the base station increase itstransmission power as the signal strength and/or quality ofcommunications received by the radioterminal decreases. Once theradioterminal 150 c moves outside the sector 121 f, a strength and/orquality measure of base station transmissions outside the sector 121 fmay decrease due to the directional nature of the base station transmitantenna(s) and due to the limited maximum EIRP (power) capability of thebase station. The base station, however, may not request any, or anysignificant, power increases from the radioterminal because at least onebase station receive antenna is directed outside the perimeter 125. Toincrease further the available return link margin between aradioterminal and a base station and thus further reduce the transmitpower of a radioterminal, at least one antenna sub-system of aperipheral and/or interior base station may be configured to receive inmore than one spatial orientation, such as in a vertical and horizontalorientation (polarization diversity reception) and, in addition or in analternative, may also be configured with more than one spatiallydistinct elements (space-diversity reception).

According to additional embodiments of the present invention, one ormore of the peripheral base stations 120 a-o may be located proximate toan airport, a navigable waterway, or other region likely to includesatellite communications terminals that may be communicating with asatellite. For example, one or more peripheral base stations 120 a-o maybe located proximate to a boundary of an airport with at least onetransmit sector of the peripheral base station(s) proximate to theboundary of the airport being directed away or substantially away fromthe airport and/or having a reduced EIRP relative to other sectors. Anarea proximate to an airport may also be served by configuring at leastone base station having at least one transmit sector whose antenna isoriented to point and/or radiate substantially in a southern direction.Providing communications service to an area proximate to an airport withat least one base station sector that is oriented to point and/orradiate in a substantially southern direction may increase and/ormaximize the antenna discrimination between a satellite terminal (thatmay also be operative with its antenna oriented in a substantiallysouthern direction due to the location of an orbital slot of ageostationary satellite) and the base station sector. (It will beunderstood that a base station sector that may be providingcommunications service to an area proximate to an airport that islocated below the earth's equator may be oriented to point and/orradiate substantially in a northern direction since relative to asatellite terminal that is located at or near the airport (below theearth's equator) a geo-stationary satellite orbital location may be at anorthern or substantially northern direction.)

The at least one transmit sector of the peripheral base station(s)proximate to the airport being directed away or substantially away fromthe airport and/or configured to radiate substantially in a southerndirection may also have a reduced EIRP value relative to other basestation sectors of the same or other base stations. At least onetransmit sector of the peripheral and/or interior base stations(s)proximate and/or distant to the airport may also be configured with aLeft-Hand Circularly Polarized (LHCP) antenna to further maximize adiscrimination between the antenna systems of the at least one transmitsector and a satellite terminal that is configured with a Right-HandCircularly Polarized (RHCP) receive antenna. Accordingly, interferencewith satellite communications terminals (aeronautical or other) that maybe operating at or near the airport resulting from base stationtransmissions can be reduced or eliminated. The interior base stationscan thus be located on a first side of the perimeter 125, and theperipheral base stations 120 a-o may be located such that the airport ison a second side of the perimeter 125.

In another example, one or more peripheral base stations 120 a-o may belocated proximate to a navigable waterway with at least one transmitsector of the peripheral base station(s) proximate to the navigablewaterway being directed away or substantially away from the navigablewaterway and/or pointed in a southern or substantially southerndirection. Providing communications service to an area proximate to anavigable waterway (in the northern hemisphere) with at least one basestation sector that is oriented in a southern or substantially southerndirection and/or is configured to radiate in a southern or substantiallysouthern direction may increase and/or maximize the antennadiscrimination between a satellite terminal (that may also be operativewith its antenna oriented in a substantially southern direction due toan orbital slot location of a geostationary satellite) and the basestation sector. (It will be understood that a base station sector thatmay be providing communications service to an area proximate to awaterway that is located below the earth's equator (in the southernhemisphere) may be oriented to point and/or radiate substantially in anorthern direction since relative to a satellite terminal that islocated at or near the waterway (below the earth's equator) ageo-stationary satellite orbital location may be at a northern orsubstantially northern direction.).

The at least one transmit sector of the peripheral base station(s)proximate to the navigable waterway being directed to radiate away orsubstantially away from the navigable waterway and/or being directed toradiate in a southern or substantially southern direction may also havea reduced EIRP value relative to other base station sectors of the sameor other base stations. At least one transmit sector of the peripheraland/or interior base station(s) proximate and/or distant to thenavigable waterway may also be configured with a Left-Hand CircularlyPolarized (LHCP) antenna to further maximize a discrimination betweenthe antenna systems of the at least one transmit sector and a satelliteterminal that is configured with a Right-Hand Circularly Polarized(RHCP) antenna. Accordingly, interference with satellite communicationsterminals at or proximate to the navigable waterway that may beoperative, for example, on boats and/or ships in the navigable waterway,resulting from peripheral and/or interior base station transmissions canbe reduced or eliminated. The interior base stations can thus be locatedon a first side of the perimeter 125, and the peripheral base stations120 a-o may be located such that the navigable waterway is on a secondside of the perimeter 125.

According to some embodiments of the present invention, the terrestrialnetwork 100 may be ancillary to a space based communications networkproviding radiotelephone communications using a satellite radiotelephonefrequency band. Moreover, base stations of the terrestrial network 100may reuse at least one frequency of the satellite frequency band, andthe space based communications network may provide communications forradioterminals when outside the terrestrial network coverage area.Accordingly, as the radioterminal 150 c moves away from the perimeter125, communications with the radioterminal 150 c may be handed off tothe space based network and/or to an alternate terrestrialcommunications network such as a cellular and/or PCS terrestrialcommunications network.

The sharing of frequencies of a satellite frequency band between a spacebased communications network and a terrestrial communications network isdiscussed, for example, in the following U.S. patent and U.S. patentpublications. Satellite radioterminal communications systems and methodsthat may employ terrestrial reuse of satellite frequencies aredescribed, for example, in U.S. Pat. No. 6,684,057 to Karabinis,entitled Systems and Methods for Terrestrial Reuse of Cellular SatelliteFrequency Spectrum; and Published U.S. Patent Application Nos. US2003/0054760 to Karabinis, entitled Systems and Methods for TerrestrialReuse of Cellular Satellite Frequency Spectrum; US 2003/0054761 toKarabinis, entitled Spatial Guardbands for Terrestrial Reuse ofSatellite Frequencies; US 2003/0054814 to Karabinis et al., entitledSystems and Methods for Monitoring Terrestrially Reused SatelliteFrequencies to Reduce Potential Interference; US 2003/0073436 toKarabinis et al., entitled Additional Systems and Methods for MonitoringTerrestrially Reused Satellite Frequencies to Reduce PotentialInterference; US 2003/0054762 to Karabinis, entitledMulti-Band/Multi-Mode Satellite Radiotelephone Communications Systemsand Methods; US 2003/0153267 to Karabinis, entitled WirelessCommunications Systems and Methods Using Satellite-Linked RemoteTerminal Interface Subsystems; US 2003/0224785 to Karabinis, entitledSystems and Methods for Reducing Satellite Feeder LinkBandwidth/Carriers In Cellular Satellite Systems; US 2002/0041575 toKarabinis et al., entitled Coordinated Satellite-Terrestrial FrequencyReuse; US 2002/0090942 to Karabinis et al., entitled Integrated orAutonomous System and Method of Satellite-Terrestrial Frequency ReuseUsing Signal Attenuation and/or Blockage, Dynamic Assignment ofFrequencies and/or Hysteresis; US 2003/0068978 to Karabinis et al.,entitled Space-Based Network Architectures for Satellite RadiotelephoneSystems; US 2003/0143949 to Karabinis, entitled Filters for CombinedRadiotelephone/GPS Terminals; US 2003/0153308 to Karabinis, entitledStaggered Sectorization for Terrestrial Reuse of Satellite Frequencies;and US 2003/0054815 to Karabinis, entitled Methods and Systems forModifying Satellite Antenna Cell Patterns In Response to TerrestrialReuse of Satellite Frequencies. All of the above referenced patentpublications and patent are assigned to the assignee of the presentinvention, and the disclosures of all of these patent publications andpatent are hereby incorporated herein by reference in their entirety asif set forth fully herein.

As shown in FIG. 4, a plurality of terrestrial communications networks100 a-d (for example, as discussed above with respect to FIG. 3) may beseparated by no-service regions such that communications services arenot provided by base stations of any of the terrestrial communicationsnetworks 100 a-d in the no-service regions. Moreover, a space-basednetwork including at least one satellite 210 may provide communicationsservice for radioterminals outside coverage areas of terrestrialcommunications networks 100 a-d and within satellite coverage areas 212a-e (such as radioterminals 150 i-m) using frequencies of a satellitefrequency band.

Frequencies of the satellite frequency band may be reused among thesatellite coverage areas 212 a-e such that, for example, the samefrequencies of the satellite frequency band may not be reused to providecommunications service in overlapping satellite coverage areas.Moreover, frequencies of the satellite frequency band may be reusedwithin the terrestrial networks 100 a-d such that, for example, the samefrequencies may not be reused in a satellite coverage area and in aterrestrial network located in the satellite coverage area. For example,the space-based network may provide communications service forradioterminals in satellite coverage area 212 a (such as radioterminal150 i) using at least a first frequency of the satellite frequency band,and the space-based network may provide communications forradioterminals in satellite coverage area 212 b (such as radioterminal150 m) using a second frequency of the satellite frequency band. Inaddition, the terrestrial network 100 d (or at least a portion thereof)is within the first satellite coverage area 212 a, and the terrestrialnetwork 100 d is outside the satellite coverage area 212 b. Accordingly,at least one base station of the terrestrial network 100 d may providecommunications service for radioterminals in a coverage area thereof(such as radioterminal 150 h) using the second frequency of thesatellite frequency band, and none of the base stations of theterrestrial network 100 d may provide communications service using thefirst frequency of the satellite frequency band.

Similarly, base stations of terrestrial networks 100 a-b may providecommunications service for radioterminals in a coverage area thereof(such as radioterminals 150 e-f) using frequencies of the satellitefrequency band other than frequencies used by the space based network toprovide communications service over satellite coverage area 212 b.Moreover, base stations of terrestrial network 100 c may providecommunications service for radioterminals in a coverage area thereof(such as radioterminal 150 g) using frequencies of the satellitefrequency band other than frequencies used by the space based network toprovide communications service over satellite coverage area 212 e.

More particularly, the satellite frequency band may include down-linkfrequencies and up-link frequencies. Down-link frequencies may be usedby the base stations of the terrestrial network(s) and by thesatellite(s) of the space based network to transmit communications toradioterminals. Up-link frequencies may be used by the base stations ofthe terrestrial network(s) and by the satellite(s) of the space basednetwork to receive communications from radioterminals. Accordingly, basestations of terrestrial network(s) may share a satellite frequency bandwith the space based network, but base stations of the terrestrialnetwork(s) may not transmit on frequencies that are received by thespace based network. Accordingly, base stations of the terrestrialnetworks sharing frequencies of the satellite frequency band may notinterfere with frequencies received by the space based network. Forexample, the space based network may transmit communications toradioterminals in the satellite coverage area 212 a using a firstfrequency of the satellite frequency band, the space based network maytransmit to radioterminals in the satellite coverage area 212 b using asecond frequency of the satellite frequency band, and at least one basestation of the terrestrial network 100 d may transmit communicationsusing the second frequency of the satellite frequency band.

Similarly, the space based network may receive communications fromradioterminals in the first satellite coverage area 212 a using a thirdfrequency of the satellite frequency band, and the space based networkmay receive communications from radioterminals in the satellite coveragearea 212 b using a fourth frequency of the satellite frequency band.Moreover, at least one base station of the terrestrial network 100 d mayreceive communications from radioterminals using the fourth frequency ofthe satellite frequency band, and none of the base stations of theterrestrial network 100 d may receive communications from radioterminalsthat are communicating therewith using the third frequency of thesatellite frequency band (at least some of the base stations ofterrestrial network 100 d may also be configured to receivecommunications from radioterminals in the first satellite coverage area212 a using the third frequency of the satellite frequency band tocommunicate with the space based network).

A first radioterminal may thus transmit communications to a peripheralbase station of the terrestrial network 100 d using the fourth frequencyand a second radioterminal in satellite coverage area 212 b may transmitto the space based network using the fourth frequency. As discussedabove with respect to FIG. 3, communications between the firstradioterminal and the terrestrial network may be terminated withoutincreasing a transmit power of the first radioterminal to a maximum, ornear maximum, level because the peripheral base station providestransmissions directed toward an interior portion of the coverage areaof the terrestrial network 100 d with greater EIRP (power) thantransmissions directed away from interior portions of the terrestrialnetwork 100 d coverage area. Accordingly, interference from the firstradioterminal with transmissions from the second radioterminal in thesatellite coverage area 212 b to the space base network may be reduced.

According to still additional embodiments of the present invention, asillustrated in FIG. 5, a terrestrial communications network 500 mayinclude a plurality of interior and peripheral base stations 510 a-i and520 a-o providing communications service for radioterminals 550 over aterrestrial network coverage area. The interior base stations 510provide communications service (both transmitting down-linkcommunications to radioterminals and receiving up-link communicationsfrom radioterminals) for radioterminals 550 in an interior portion ofthe terrestrial network coverage area. In contrast, the peripheral basestations 520 may only receive up-link communications fromradioterminals. Stated in other words, at least one of the peripheralbase stations 520 may be a receive-only base station.

More particularly, at least one of the interior base stations 510 maydefine a plurality of sectors surrounding the at least one interior basestation, and the at least one interior base station(s) 510 may directtransmissions to all sectors surrounding the interior base station sothat transmissions are directed over a 360 degree pattern surroundingthe respective interior base station. For example, one of the interiorbase stations may include directional transmit antennas configured toprovide transmissions over a 120 degree sector, and the base station(s)may include at least three such directional antennas so thattransmissions are directed over three 120 degree sectors to cover a 360degree pattern surrounding the base station. In addition or in analternative, one or more interior base stations 510 may includeomnidirectional antennas and/or directional antennas. At least one ofthe interior base stations may also be configured so that transmissionsare directed to a pattern of less than 360 degrees surrounding the atleast one interior base station. Complete transmission patterns and/orsectors are not shown for the interior base stations 510 of FIG. 5 forthe sake of clarity.

As discussed above, at least one of the peripheral base stations 520 maybe a receive-only base station(s). More particularly, peripheral basestations may include one or more receive antennas providing receptioncapability to at least one sector, such as a 120 degree sector.Moreover, the receive antenna(s) on a peripheral base station 520 may beoriented such that reception for the peripheral base station 520 isdirected over a sector oriented substantially toward interior portionsof the terrestrial network coverage area with greater sensitivity thanis directed over a sector oriented substantially away from interiorportions of the terrestrial network coverage area. In an alternative, aperipheral base station 520 may include receive antennas directed overtwo or more sectors oriented substantially toward interior portions ofthe terrestrial network coverage area, and/or a peripheral base station520 may include receive antennas directed over a plurality of sectorscovering a 360 degree pattern surrounding the peripheral base station520. An engineered boundary of coverage areas of the interior basestations 510 may define a perimeter 525 (illustrated by the dotted lineof FIG. 5) of the terrestrial network coverage area such that interiorbase stations 510 are located on one side of the perimeter 525 and noton the other side of the perimeter 525. In an alternative or inaddition, one or more of the peripheral base stations may include one ormore omnidirectional receive antennas and/or one or more directionalreceive antennas.

Accordingly, interior and exterior base stations 510 and 520 may providecommunications services for radioterminals in a coverage area and/orsector thereof using, for example, FDM/FDMA (frequency divisionmultiplexed/multiple access), TDM/TDMA (time divisionmultiplexed/multiple access), CDM/CDMA (code divisionmultiplexed/multiple access) architecture, and/or OFDM/OFDMA (orthogonalfrequency division multiplexed/multiple access). Moreover, the basestations of the terrestrial communications network 500 may employ afrequency reuse and/or spreading code reuse pattern to increase anefficiency of frequency usage and/or capacity and/or reduceinterference. For example, each base station may have a relatively smallcoverage area and/or sector and adjacent base stations and/or sectorsmay use different frequencies and/or spreading codes to reduceinterference therebetween.

Communications service for a radioterminal 550 a in an interior portionof the terrestrial network coverage area may be provided by an interiorbase station 510 c as illustrated in FIG. 5. As the radioterminal 550 amoves within the terrestrial network coverage area during acommunication such as a radiotelephone conversation, communicationsservices for the radioterminal 550 a may be handed off from one sectorof base station 510 c to another sector of base station 510 c, and/or tosectors of other interior and/or peripheral base stations. Moreparticularly, a down-link for transmissions to the radioterminal 510 aand an up-link for transmissions from the radioterminal may be providedby one or more interior base stations as long as the radioterminal iswithin a coverage area of one of the interior base stations.

As shown in FIG. 5, the engineered coverage areas of interior basestations 510 may appear to have fixed boundaries defined by the transmitsectors of the respective transmit antennas. As will be understood,however, radiation patterns generated by transmit antennas, such as bythe transmit antennas of the interior base station 510 g, may havesufficient energy to support transmissions to a radioterminal 550 boutside the perimeter 525 of the terrestrial network engineered coveragearea. As discussed above, the peripheral base station 520 g may includereceive antennas supporting robust link reception of communications fromthe mobile terminal 550 b outside the perimeter 525.

Accordingly, communications service for the radioterminal 550 b mayinitially be provided by the interior base station 510 g, but theradioterminal 550 b may then move outside the engineered coverage areaof interior base station 510 g, outside the perimeter 525, and away fromthe terrestrial network engineered coverage area. According toembodiments of the present invention, transmissions from the basestation 510 g to the radioterminal 550 b may continue to be provided bythe transmit antenna(s) of interior base station 510 g, and the qualityof the communications received by the radioterminal 550 b maydeteriorate. A relatively high quality of communications received by theperipheral base station 520 g from the radioterminal 550 b, however, maybe maintained as the radioterminal 550 b moves outside the engineeredcoverage area of interior base station 510 g. Accordingly,communications service for the radioterminal 550 b will most likely beterminated due to deterioration in the down-link from the interior basestation 510 g to the radioterminal 550 b before significantdeterioration in the up-link from the radioterminal 550 b to the basestation 520 g occurs. (In an alternative, base station 520 g and basestation 510 g may be configured to combine their correspondingreceptions from a radioterminal such as their receptions fromradioterminal 550 b.) Accordingly, down-link communications to theradioterminal 550 b and up-link communications from the radioterminalmay be provided using different base stations when the radioterminal 550b is outside the engineered terrestrial network service perimeter 525.

By providing receive-only peripheral base stations outside the perimeter525 that can receive communications from a radioterminal, communicationswith the radioterminal can be terminated without causing theradioterminal to boost its transmit power to a maximum, or a nearmaximum, level before termination. More particularly, in a closed looppower control system, a terrestrial network infrastructure such as, forexample, a base station (or base stations) may request that theradioterminal increase its transmission power as the quality ofcommunications received by the infrastructure (base station or basestations) decreases, and similarly, the radioterminal may request thatan infrastructure, such as, for example, a base station, providingcommunications information to the radioterminal increase itstransmission power as the quality of communications received by theradioterminal decreases. Once the radioterminal 550 b movessubstantially outside the engineered coverage area of interior basestation 510 g, and because the EIRP (power) from the base station 510 gmay be limited to a predetermined maximum, a strength and/or qualitymeasure of base station transmissions outside the engineered coveragearea thereof may decrease. An infrastructure of the terrestrialcommunications network, however, such as base station 510 g, may notrequest any, or any significant, power increases for transmissions fromthe radioterminal 550 b that is outside of the network's engineeredlimit(s) because receive antennas from the base station 520 g (and/or510 g) may be configured to cover the areas outside of perimeter 525 notcovered by transmit and/or receive antennas of base station 510 g inaccordance with the system's engineered limits and/or parameters. Thatis, for at least some areas outside of perimeter 525 base station 510 gon its own, without aid of peripheral base station 520 g, may notprovide X dB (i.e., 18 dB) of return-link structural attenuation margin.

According to additional embodiments of the present invention, one ormore of the peripheral base stations 520 a-o may be located proximate toan airport, a navigable waterway, or other region likely to includesatellite communications terminals. For example, one or more peripheralbase stations 520 a-o may be located proximate to a boundary of anairport with the peripheral base station(s) being located between one ormore of the interior base stations 510 a-i and the airport. Accordingly,interference with satellite communications terminals in airplanes at theairport resulting from base station transmissions of the terrestrialnetwork 500 can be reduced. The interior base stations 510 a-i can thusbe located on a first side of the perimeter 525, and the peripheral basestations 520 a-o may be located such that the airport is on a secondside of the perimeter 525. Moreover, one or more of the peripheral basestations may be between the perimeter 525 and the airport. In anotherexample, one or more peripheral base stations 520 a-o may be locatedproximate to a navigable waterway with one or more of the peripheralbase stations 520 a-o being located between one or more of the interiorbase stations 510 a-i and the waterway. Accordingly, interference withsatellite communications terminals on boats and/or ships in thenavigable waterway resulting from base station transmissions of theterrestrial network 500 can be reduced. The interior base stations canthus be located on a first side of the perimeter 525, and the peripheralbase stations 520 a-o may be located such that the navigable waterway ison a second side of the perimeter 525. Moreover, one or more of theperipheral base stations 520 a-o may be between the perimeter 525 andthe waterway.

According to some embodiments of the present invention, the terrestrialnetwork 500 may be ancillary to a space based communications networkproviding radiotelephone communications using a satellite radiotelephonefrequency band. Moreover, base stations of the terrestrial network 500may reuse at least one frequency of the satellite frequency band, andthe space based communications network may provide communications forradioterminals when outside the terrestrial network coverage area.Accordingly, as the radioterminal 550 b moves away from the perimeter525, communications with the radioterminal 550 b may be handed off tothe space based network and/or to an alternative terrestrialcommunications network such as a cellular and/or PCS terrestrialcommunications network.

The sharing of frequencies of a satellite frequency band between a spacebased communications network and a terrestrial communications network isdiscussed, for example, in the following U.S. patent and U.S. patentpublications. Satellite radioterminal communications systems and methodsthat may employ terrestrial reuse of satellite frequencies aredescribed, for example, in U.S. Pat. No. 6,684,057 to Karabinis,entitled Systems and Methods for Terrestrial Reuse of Cellular SatelliteFrequency Spectrum; and Published U.S. Patent Application Nos. US2003/0054760 to Karabinis, entitled Systems and Methods for TerrestrialReuse of Cellular Satellite Frequency Spectrum; US 2003/0054761 toKarabinis, entitled Spatial Guardbands for Terrestrial Reuse ofSatellite Frequencies; US 2003/0054814 to Karabinis et al., entitledSystems and Methods for Monitoring Terrestrially Reused SatelliteFrequencies to Reduce Potential Interference; US 2003/0073436 toKarabinis et al., entitled Additional Systems and Methods for MonitoringTerrestrially Reused Satellite Frequencies to Reduce PotentialInterference; US 2003/0054762 to Karabinis, entitledMulti-Band/Multi-Mode Satellite Radiotelephone Communications Systemsand Methods; US 2003/0153267 to Karabinis, entitled WirelessCommunications Systems and Methods Using Satellite-Linked RemoteTerminal Interface Subsystems; US 2003/0224785 to Karabinis, entitledSystems and Methods for Reducing Satellite Feeder LinkBandwidth/Carriers In Cellular Satellite Systems; US 2002/0041575 toKarabinis et al., entitled Coordinated Satellite-Terrestrial FrequencyReuse; US 2002/0090942 to Karabinis et al., entitled Integrated orAutonomous System and Method of Satellite-Terrestrial Frequency ReuseUsing Signal Attenuation and/or Blockage, Dynamic Assignment ofFrequencies and/or Hysteresis; US 2003/0068978 to Karabinis et al.,entitled Space-Based Network Architectures for Satellite RadiotelephoneSystems; US 2003/0143949 to Karabinis, entitled Filters for CombinedRadiotelephone/GPS Terminals; US 2003/0153308 to Karabinis, entitledStaggered Sectorization for Terrestrial Reuse of Satellite Frequencies;and US 2003/0054815 to Karabinis, entitled Methods and Systems forModifying Satellite Antenna Cell Patterns In Response to TerrestrialReuse of Satellite Frequencies. All of the above referenced patentpublications and patent are assigned to the assignee of the presentinvention, and the disclosures of all of these patent publications andpatent are hereby incorporated herein by reference in their entirety asif set forth fully herein.

As shown in FIG. 6, a plurality of terrestrial communications networks500 a-d (as discussed above with respect to FIG. 5) may be separated byno-service regions such that communications services are not provided bybase stations of any of the terrestrial communications networks 500 a-din the no-service regions. Moreover, a space-based network including atleast one satellite 610 may provide communications service forradioterminals outside coverage areas of terrestrial communicationsnetworks 500 a-d and within satellite coverage areas 612 a-e (such asradioterminals 550 i-m) using frequencies of a satellite frequency band.

Frequencies of the satellite frequency band may be reused among thesatellite coverage areas 612 a-e such that, for example, the samefrequencies of the satellite frequency band are not reused to providecommunications service in overlapping satellite coverage areas.Moreover, frequencies of the satellite frequency band may be reusedwithin the terrestrial networks 500 a-d such that, for example, the samefrequencies are not reused in a satellite coverage area and in aterrestrial network located in the satellite coverage area. For example,the space-based network may provide communications service forradioterminals in satellite coverage area 612 a (such as radioterminal550 i) using at least a first frequency of the satellite frequency band,and the space-based network may provide communications forradioterminals in satellite coverage area 612 b (such as radioterminal550 m) using a second frequency of the satellite frequency band. Inaddition, the terrestrial network 500 d (or at least a portion thereof)is within the first satellite coverage area 612 a, and the terrestrialnetwork 500 d is outside the satellite coverage area 612 b. Accordingly,at least one base station of the terrestrial network 500 d may providecommunications service for radioterminals in a coverage area thereof(such as radioterminal 550 h) using the second frequency of thesatellite frequency band, and none of the base stations of theterrestrial network 500 d may provide communications service using thefirst frequency of the satellite frequency band.

Similarly, base stations of terrestrial networks 500 a-b may, forexample, provide communications service for radioterminals in a coveragearea thereof (such as radioterminals 550 e-f) using frequencies of thesatellite frequency band other than frequencies used by the space basednetwork to provide communications service over satellite coverage area612 b. Moreover, base stations of terrestrial network 500 c may, forexample, provide communications service for radioterminals in a coveragearea thereof (such as radioterminal 550 g) using frequencies of thesatellite frequency band other than frequencies used by the space basednetwork to provide communications service over satellite coverage area612 e.

More particularly, the satellite frequency band may include down-linkfrequencies and up-link frequencies. Down-link frequencies may be usedby the base stations of the terrestrial network(s) and by thesatellite(s) of the space based network to transmit communications toradioterminals. Up-link frequencies may be used by the base stations ofthe terrestrial networks and by the satellite(s) of the space basednetwork to receive communications from radioterminals. Accordingly, basestations of terrestrial networks may share a satellite frequency bandwith the space based network, but base stations of the terrestrialnetworks may not, for example, transmit on frequencies that are receivedby the space based network. Accordingly, base stations of theterrestrial networks sharing frequencies of the satellite frequency bandmay not interfere with frequencies received by the space based network.For example, the space based network may transmit communications toradioterminals in the satellite coverage area 612 a using a firstfrequency of the satellite frequency band, the space based network maytransmit to radioterminals in the satellite coverage area 612 b using asecond frequency of the satellite frequency band, and at least one basestation of the terrestrial network 500 d may transmit communicationsusing the second frequency of the satellite frequency band.

Similarly, the space based network may receive communications fromradioterminals in the first satellite coverage area 612 a using a thirdfrequency of the satellite frequency band, and the space based networkmay receive communications from radioterminals in the satellite coveragearea 612 b using a fourth frequency of the satellite frequency band.Moreover, at least one base station of the terrestrial network 500 d mayreceive communications from radioterminals that it is transmittingcommunications to using the fourth frequency of the satellite frequencyband, and none of the base stations of the terrestrial network 500 d mayreceive communications from radioterminals that are communicatingtherewith using the third frequency of the satellite frequency band. (Atleast some of the base stations of the terrestrial network 500 d mayalso be configured to receive communications from radioterminals in thefirst satellite coverage area 612 a using the third frequency of thesatellite frequency band to communicate with the space based network.)

A first radioterminal may thus transmit communications to a peripheralbase station of the terrestrial network 500 d using the fourth frequencyand a second radioterminal in satellite coverage area 612 b may transmitto the space based network using the fourth frequency. As discussedabove with respect to FIG. 5, communications between the firstradioterminal and the terrestrial network may be terminated withoutincreasing a transmit power of the first radioterminal to a maximum, ornear maximum, level because the peripheral receive-only base stationprovides at least one receive antenna directed toward an interiorportion of the coverage area of the terrestrial network 500 d such as toprovide a high-quality return link for the first radioterminal.Accordingly, interference from the first radioterminal with transmissionfrom the second radioterminal in the satellite coverage area 612 b tothe space base network can be reduced.

Moreover, elements of embodiments discussed above with respect to FIGS.3-6 may be combined. For example, the terrestrial communicationsnetworks 100 of FIGS. 3 and/or 4 may include one or more receive-onlybase stations configured to receive communications from radioterminalsoutside the perimeter 125 (as discussed above with respect to peripheralbase stations 520 of FIG. 5) thereby further enhancing up-link qualityas compared to down-link quality outside the perimeter 125. In additionor in an alternative, a receive-only base station may be substituted forone or more of the peripheral base stations 120 of FIGS. 3 and/or 4.

Similarly, the terrestrial communications networks 500 of FIGS. 5 and 6may include one or more base stations providing transmissions directedtoward an interior portion of the terrestrial network coverage area withgreater power than transmissions directed away from interior portions ofthe terrestrial network coverage area (as discussed above with respectto peripheral base stations 120 of FIG. 3). For example, a peripheralbase station 120 as discussed above with respect to FIG. 3 may besubstituted for one or more of the interior base stations 510 a-b, 510d, 510 e-g, or 510 h-i along the perimeter 525. In addition or in analternative, a peripheral base station 120 as discussed above withrespect to FIG. 3 may be substituted for one or more of the peripheralbase stations 520 of FIG. 5.

In the drawings and specification, there have been disclosed typicalembodiments of the invention and, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being set forth inthe following claims. Moreover, while particular systems are discussedabove with respect to the figures, analogous methods are also includedin the present invention.

1. A terrestrial communications network that is configured to wirelesslycommunicate with a plurality of radiotelephones, the terrestrialcommunications network comprising: a plurality of base stations that areconfigured to wirelessly communicate with the plurality ofradiotelephones, the plurality of base stations including at least onebase station that is configured to transmit information to at least oneradiotelephone using a circularly polarized antenna.
 2. A terrestrialcommunications network according to claim 1 wherein the at least onebase station receives information from at least one radiotelephone usinga polarization diversity and/or a space diversity antenna configuration.3. A terrestrial communications network according to claim 1 wherein theat least one base station transmits information using a FDM/FDMA,TDM/TDMA, CDM/CDMA and/or OFDM/OFDMA air interface protocol and/orarchitecture.
 4. A terrestrial communications network according to claim1 wherein the at least one base station transmits information using atleast one frequency that is also used by a satellite system.
 5. Aterrestrial communications network according to claim 1 wherein thecircularly polarized antenna is configured to transmit usingsubstantially Left-Hand Circular Polarization (LCHP).
 6. A wirelesscommunications method comprising: configuring a plurality of basestations to wirelessly communicate with a plurality of radiotelephones;configuring at least one base station of the plurality of base stationswith a circularly polarized antenna; and transmitting information to atleast one radiotelephone using the circularly polarized antenna.
 7. Amethod according to claim 6 further comprising: receiving information atthe at least one base station from at least one radiotelephone using apolarization diversity and/or a space diversity antenna configuration.8. A method according to claim 6 wherein transmitting informationcomprises: using a FDM/FDMA, TDM/TDMA, CDM/CDMA and/or OFDM/OFDMA airinterface protocol and/or architecture.
 9. A method according to claim 6wherein transmitting information comprises: using at least one frequencythat is also being used by a satellite system.
 10. A method according toclaim 6 wherein the circularly polarized antenna is a left-handcircularly polarized antenna.
 11. A method according to claim 6 whereintransmitting information to the at least one radiotelephone comprisestransmitting information to the at least one radiotelephone using thecircularly polarized antenna using substantially Left-Hand CircularPolarization (LHCP).